The present invention relates to plastic injection moulding equipment in general and, more in particular, an injection nozzle for such equipment, of the type comprising a body with a central passageway and a nozzle tip including an internal hollow element made of a material with high thermal conductivity and an external hollow element made of a material with a lower thermal conductivity.
An injection nozzle of this type is described and illustrated, for example, in European Patent EP-B-0633118 in the name of GELLERT, according to which the external hollow element presents a thread at one end that can engage with a corresponding thread on the injector body and, at the other end, a part providing sealed contact with the injection mould to which the injector is operatively associated. The internal hollow element is placed between the said central passageway and the external hollow element.
In the injector nozzle described in EP-B-0633118, the internal hollow element is locked and restrained relative to the body of the injector nozzle by the same external hollow element itself, which thus functions as an axial stop device for the internal hollow element. With this device, the external hollow element is in direct contact with the internal hollow element along wide areas of its surface, with the consequent transmission of a significant amount of heat due to conduction. Heat is thus transmitted from the internal hollow element, through the sealed contact part between the external hollow element and the injection mould to which the injection nozzle is applied, to the mould itself, which constitutes an undesired effect. Instead, it is desirable to reduce such heat transmission as much as possible for the efficiency of the injection moulding process.
In order to achieve this object, the subject of the invention is an injection nozzle of the type defined at the beginning, the essential characteristic of which resides in the fact that the internal hollow element is connected to the body of the injector independently of the external hollow element, and in the fact that a space of mutual separation is defined between the said external hollow element and the said internal hollow element.
The space of mutual separation provides an air gap, due to which there is no direct contact between the internal hollow element and the external hollow element and hence the transmission of heat from the injection nozzle to the mould is considerably reduced.
In accordance with a preferred form of embodiment of the invention, the internal hollow element is provided with a thread that engages with a corresponding thread on the body of the injector. In addition, the contact part of the external hollow element, which can beneficially be elastically sprung, has advantageously a substantially spherical surface and, between this contact part and the remainder of the external hollow element, a reduced-section annular part, which also contributes to reducing the transmission of heat to mould, can be provided to advantage.